Composite multilayer seal for pem fuel cell applications and method for constructing the same

ABSTRACT

A composite seal having a multilayer elastomeric construction and method for constructing the same is provided. More specifically, the present invention provides a composite seal comprised of a low-durometer elastomer compliant layer coated with, or alternatively encapsulated by, a thin protective layer for securely sealing a bipolar plate and a membrane electrode assembly of a fuel cell. The elastomer compliant layer is preferably a silicone constituent and the thin coat protective layer is preferably a fluoroelastomer or fluoropolymer constituent suitable for bonding to the elastomer compliant layer. The foregoing layers constructing the composite seal are preferably deposited directly onto the aforementioned fuel cell components along a predetermined periphery. The resulting composite seal is thin in construction, resistive to undesired chemical and thermal reactions and provides the necessary compressive compliance without undue stress on the fuel cell assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/248,038, filed Oct. 8, 2008, which claims priority to U.S.Provisional Patent Application No. 60/978,381, filed Oct. 8, 2007, thesubject matter of which are incorporated by reference herein in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to seals for use in fuel cellapplications. More particularly, the present invention relates to acomposite seal comprising a multiple layer elastomeric construction forproviding superior sealing performance and durability in proton exchangemembrane (PEM) fuel cell applications.

2. Description of the Prior Art

A PEM fuel cell is assembled from multiple component layers, theessential component layers including a reactive membrane and a pluralityof gas diffusion layers (GDL) making up the membrane electrode assembly(MEA) and opposing bipolar plates (one for enclosing the anode side andanother for enclosing the cathode side of the cell). The MEA isinterposed between the anode and cathode bipolar plates. Additionalcomponents may be used to help draw hydrogen fuel and oxygen gas intothe fuel cell assembly and to conduct the electrical current generatedby their corresponding interaction.

The use of PEM fuel cells as a means for generating electrical currentis achieved through a controlled electrochemical reaction, driven by theMEA, between the hydrogen fuel and oxygen gas. More specifically,hydrogen is permitted to flow into the fuel cell on the anode side andis catalytically split into hydrogen ions (i.e., protons) and electrons.The ions permeate across the MEA to the cathode side, while the freedelectrons flow through an external circuit coupled to the anode andcathode sides of the fuel cell to drive a load. As the hydrogen ionspermeate through the MEA, oxygen is permitted to flow on the cathodeside to combine with the electrons traversing the circuit load and thehydrogen ions permeating through the MEA. The recombination of theseelements results in the formation of water and heat.

To ensure proper containment of the aforementioned electrochemicalreaction, various gasket constructions are used to seal the periphery ofthe MEA interposed between anode and cathode bipolar plates. Many ofthese gasket constructions are known to utilize silicone basedelastomers. Whereas silicone based elastomers are typically used in lowtemperature (i.e., less than 180° C.) fuel cell applications, their usein high temperature fuel cell applications is problematic due to theirvulnerability to deterioration over time and subsequent interaction witha fluorene constituent, as well as the high pH values, commonlyassociated within a fuel cell environment. The use of silicone in lowtemperature fuel cell applications can be problematic as well in thatits use in low temperature fuel cell applications has the potential forlong term permeation of low molecular weight gases and materials throughthe silicone body due to its inherently porous molecular structure.Despite the foregoing, silicone remains the current standard even thoughin some cases it may not be the preferred sealing material.

Fluoroelastomer fluoropolymers, having a more resilient structure, arepreferred for sealing applications. Fluoro materials, however, generallydo not possess durometer values less than 55 Shore A, which presents anadditional problem with respect to providing the necessary compliancefor sealing anode and cathode bipolar plates to an adjoining MEA withoutresulting in undue stress on components of the fuel cell assembly. Thisis particularly a concern when dealing with bipolar plates comprised ofinherently brittle graphite constructions.

Accordingly, it is desirable to provide an improved sealing solution,said sealing solution providing the necessary chemical and thermalresistance properties, as well as the necessary compressive complianceproperties, needed for use in both low and high temperature yieldingfuel cell applications. In addition to providing a resilient andstructurally compliant sealing solution, it is also desirable tominimize misalignment or sealing vulnerabilities commonly associatedwith loose die-cut or free molded gaskets by providing a more integralsealing solution.

SUMMARY OF THE INVENTION

The present invention proposes a novel composite seal suitable for usein fuel cell applications having a wide array (low and high) oftemperature yields. The composite seal of the present invention iscomprised of a multiple layer elastomeric construction having anelastomer compliant layer, which may serve as a core or base layer thatis encapsulated or coated, respectively, by a thin protective layer.These proposed composite multilayer constructions provide a significantimprovement over existing sealing applications.

In an encapsulated embodiment of the present invention, the protectivelayer is disposed directly onto a peripheral surface of the bipolarplate, the MEA, the GDL or a combination thereof. After curing theprotective layer, the elastomer compliant layer is disposed thereon andcured. To complete the encapsulation process, which has the elastomercompliant layer serving as the core layer, a final disposition of theprotective layer is applied over the elastomer compliant layer andcured. Alternatively, in a non-encapsulated embodiment of the presentinvention, the elastomer compliant layer is first disposed directly ontoa peripheral surface of the bipolar plate, the MEA, the GDL or acombination thereof. After curing, the elastomer compliant layer iscoated with the protective layer and then subjected to a final curingstage.

When applying the foregoing layers, the elastomer compliant layer ispreferably liquid deposited directly onto a metal, graphite or polymersubstrate (e.g., along the periphery of the graphite bipolar plate, theMEA, the GDL or a combination thereof) or, alternatively, over theprotective layer previously disposed on the substrate, to minimizesources of leakage common to that of traditional die-cut or moldedgaskets. The direct deposit application onto the substrate additionallyhelps in minimizing the overall thickness of the composite seal. Thedeposition of the aforementioned layers may be provided by spray, offsettransfer via a brush or roller, or by direct metering to the surface ina controlled volumetric manner, including molding.

The elastomer compliant layer is preferably a low-durometer elastomer,such as a silicone-based or fluorosilicone-based constituent. Theprotective layer is preferably a fluoroelastomer (i.e., Viton, Fluorel,Dai-el, Aflas, Technoflon, etc.) or fluoropolymer (i.e., Poly TetraFluoro Ethylene (PTFE), Per Fluor Alkoxy (PFA), Fluoro EthylenePropylene (FEP), etc.) or any other suitable combination offluoroelastomers or fluoropolymers suitable for adhesion to the lowdurometer elastomer compliant layer or aforementioned corresponding fuelcell component surfaces. The thin coat protective layer provides thenecessary chemical and thermal resistance needed to withstand the activeinternal environment of the fuel cell that would be detrimental to thefunctionality of the elastomer compliant layer, while the widelow-durometer range of the elastomer compliant layer serves to providethe required compressive compliance needed for effective sealing of thefuel cell component layers.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention willbecome apparent upon consideration of the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like reference characters refer to like parts throughout, and inwhich:

FIG. 1 is a disassembled view of known PEM fuel cell arrangements.

FIG. 2 is a partial disassembled view of a PEM fuel cell arrangement,particularly the membrane electrode assembly (MEA) and a bipolar plateof a PEM fuel cell, and a composite seal provided along the periphery ofthe bipolar plate and MEA in accordance with preferred embodiments ofthe present invention

FIGS. 3A-3C illustrate a variety of bipolar plates for use in PEM fuelcell applications having the composite seal deposited thereon inaccordance with preferred embodiments of the present invention.

FIGS. 4A-4C illustrate, respectively, various bead sizes andconfigurations, a cross-sectional view of a non-encapsulated multilayerelastomer construction of the composite seal along a periphery of abipolar plate and an encapsulated multilayer elastomer construction ofthe composite seal along a periphery of a bipolar plate in accordancewith preferred embodiments of the present invention.

FIGS. 5A-5B is a flowchart illustrating the process of depositing andconstructing the composite multilayer seal in accordance with preferredembodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed at a novel composite multilayer sealfor PEM fuel cell applications. For purposes of clarity, and not by wayof limitation, illustrative views of the novel composite multilayer sealand methods for constructing the same are described with reference tothe aforementioned accompanying drawings.

In FIG. 1, a disassembled view of a known fuel cell arrangement 100 isprovided. Fuel cell arrangement 100 is comprised of a PEM (not shown) atits core for conducting only positively charged ions. The PEM is fixedbetween a pair of catalysts, wherein a first catalyst is provided on oneside of the PEM core for facilitating an anode reaction (i.e.,H₂→2H⁺+2e⁻) and a second catalyst is fixed on an opposing side of thePEM core for facilitating the cathode reaction (i.e., O₂+4e⁻+4H⁺→2H₂O).The most common catalyst employed in the construction of PEM fuel cellsis platinum powder or nanoparticles. Platinum is thinly coated onto asingle side of a porous backing, such as carbon cloths (or paper) 102 aand 102 b, wherein the platinum-coated sides of carbon cloths 102 a and102 b are positioned in a direction facing the PEM core. Platinum-coatedcarbon cloths 102 a and 102 b are commonly referred to as the electrodecatalyst layers, wherein platinum-coated carbon cloth 102 a drives theanode (i.e., negative) side of the reaction and platinum-coated carboncloth 102 b drives the cathode (i.e., positive) side of the reaction.The PEM core and electrode catalyst layers seated on opposing sides ofthe PEM core are collectively referred to as a membrane electrodeassembly (MEA) 104.

MEA 104 is enclosed between two bipolar plates. A bipolar plate 106 a isprovided on the anode side, for equally dispersing hydrogen fuel viaetched channel 107 a, and a bipolar plate 106 b, for equally dispersingoxygen gas via etched channel 107 b, is provided on the cathode side offuel cell arrangement 100. Etched channels 107 a and 107 b are commonlyreferred to as flow fields. Bipolar plates 106 a and 106 b are typicallyconstructed of a lightweight, gas-impermeable, electron-conductivematerial (e.g., graphite) that may be coupled to drive a load (notshown).

Affixed between the anode side of MEA 104 and corresponding bipolarplate 106 a and the cathode side of MEA 104 and corresponding bipolarplate 106 b are, respectively, gaskets 105 a and 105 b. Gaskets 105 aand 105 b provide a means for sealing the hydrogen fuel and oxygen gasbeing dispersed within the confines of fuel cell arrangement 100.However, gaskets 105 a and 105 b are prone to a reduction in physicalperformance due to chemical and thermal aging, which tends to reduce theability to provide adequate sealing and necessary compressivecompliance. Additionally, the introduction of constituents from withinthe chemical makeup of these gaskets has the potential to poison thefunctionality of the internal PEM fuel cell components. Each of thesevulnerabilities take away from the efficiency of the cell and, in somecases, can render the cell completely inadequate for its intendedpurpose. As the efficiency and power output of fuel cells becomes a moreviable source for alternative energy, these die-cut or molded gasketsare proving to be unreliable sealing solutions and, in many cases,actually constrain the development of more advanced PEM fuel cellstacks.

The present invention proposes a more resilient, yet adaptable, sealingsolution. Referring to FIG. 2, a partial view of a fuel cell arrangement200 is illustrated. In fuel cell arrangement 200, an MEA 202 and abipolar plate 204 are provided. Rather than layering traditional die-cutor molded gasket between multiple fuel cell layers, as depicted in fuelcell arrangement 100 of FIG. 1, the present invention proposes the useof a novel gasket construction that can be directly deposited to theprimary components of a fuel cell arrangement. Applied along theperiphery of bipolar plate 204, MEA 202, GDL 203 or, alternatively, acombination thereof (depending on varying sealing solution needs) is acomposite seal 206. For purposes of brevity and illustration, and not byway of limitation, the forthcoming description primarily describes theapplication of composite seal 206 with respect to bipolar plate 204. Onewith skill in the art, however, will understand that the nature ofcomposite seal 206, the preferred embodiments of which are described indetail herein, is equally applicable to the peripheral surface of otheressential fuel cell component parts, as illustrated in FIG. 2.

Composite seal 206 may be deposited directly along the periphery ofbipolar plate 204 in any suitable configuration to accommodate forvarious sizes, flow field designs and fuel or gas feed openings inbipolar plate 204. For example, in FIG. 2 an opening 205 is provided.When applying composite seal 206 onto bipolar plate 204, a pre-definedapplication operation best suited for this particular design of bipolarplate 204 may be deployed. In the representative embodiment provided inFIG. 2, composite seal 206 is provided along the outer and innerperiphery of bipolar plate 204, as well as around opening 205 to ensuresecure receipt and containment of, for example, hydrogen fuel or oxygengas. Alternatively, as previously described, composite seal 206 can beplaced directly on the surface of MEA 202, either at its outer peripheryor at the periphery interface with GDL 203 as illustrated in FIG. 2.These alternative applications of composite seal 206 can serve tofurther isolate the cell system environment and eliminate, orsignificantly reduce, the need for a large section of the polymerportion of the membrane to extend beyond the active surface area of GDL203. By eliminating the need for a die-cut or molded gasket and,instead, employing the use of composite seal 206 directly along theperiphery of bipolar plate 204, or any other of the aforementionedcomponent parts, possible sources of leakage common with traditionalgaskets are significantly reduced and an improved assembly technique isfacilitated.

The use of various bipolar plate designs 302 a and 302 b, as illustratedin FIGS. 3A and 3B, are expected as technological advances are made inPEM fuel cell applications. In view of the plurality of designparameters that are anticipated, an adaptable application process isproposed for directly depositing composite seal 206 along the periphery,or any alternate configuration, of bipolar plate 204 or MEA 202. In apreferred embodiment of the present invention, as illustrated in FIG.3C, an applicator 304 controlled, for example, by a correspondingprogrammable liquid delivery system (not shown) may be employed forprecise application of any suitable constituent of composite seal 206onto bipolar plate 204. This controlled delivery can be deployed via adirect contact method, such as brushing, wheel or pad transfer, or byatomization of the disposed liquid solution.

Composite seal 206, as referenced in FIG. 2 and FIGS. 3A-3C, is amultiple layer elastomeric construction, wherein its primaryconstituents may be deposited on bipolar plate 204 or MEA 202 in aplurality of bead sizes, numbers and configurations, as illustrated inFIG. 4A, to accommodate a plurality of bipolar plate and MEAapplications and designs. Bead widths and heights of composite seal 206are carefully determined, based in part on particular bipolar platedesigns, construction and proposed applications, to provide a highlydesirable thin and durable seal. Bead width and height of composite seal206 may be applied in a wide range of sizes and height-to-width ratios.A plurality of height-to-width ratios, including a listing ofcorresponding bead heights and widths, are provided in FIG. 4A.

A cross-sectional view of composite seal 206, as applied along theperiphery of bipolar plate 204, is illustrated in FIGS. 4B and 4C. Anon-encapsulated application of composite seal 206 is illustrated inFIG. 4B, wherein the multiple layer elastomeric construction ofcomposite seal 206 is comprised of a silicone base layer 402 a and athin fluoroelastomer protective layer 402 b overlaid thereon. Anencapsulated application of composite seal 206 is illustrated in FIG.4C, wherein the multiple layer elastomeric construction of compositeseal 206 is comprised of a silicone core layer 404 a having a thinfluoroelastomer/fluoropolymer protective layer 404 b underlying and athin fluoroelastomer/fluoropolymer protective layer 404W overlaying thesurface of silicone core layer 404 a. The hardness of silicone layers402 a and 404 a and protective layers 402 b and 404 b/404 b′ may range,respectively, between 15 to 65 Shore A and 50 to 80 Shore A. Thethickness of protective layer 402 b and 404 b/404 b′ may range between10 and 100 microns.

In accordance with the non-encapsulated embodiment illustrated in FIG.4B, silicone base layer 402 a is first dispensed and cured along theperiphery, or any alternate configuration desired, of bipolar plate 204.Silicone base layer 402 a may be comprised of a dimethyl, phenyl orblended combination thereof. Dimethyl and phenyl are preferred due totheir wide range of viscosities, inherent stability and chemicalresistance. Thereafter, fluoroelastomer/fluoropolymer protective layer402 b is bonded and cured to silicone base layer 402 a to form compositeseal 206. Alternatively, in the encapsulated embodiment illustrated inFIG. 4C, a thin fluoroelastomer/fluoropolymer protective layer 404 b isfirst dispensed and cured along the periphery, or any alternateconfiguration desired, of bipolar plate 204. Silicone core layer 404 ais then deposited and cured over protective layer 404 b and coated witha second fluoroelastomer/fluoropolymer protective layer 404W, completelyencapsulating silicone core layer 404 a. Similar to the compositemultilayer construction described in connection with thenon-encapsulated embodiment, this alternate embodiment also provides forthe same improved resiliency and compressive compliance attributes whencompared to that of traditional die-cut and molded gasket constructions.

Fluoroelastomer/fluoropolymer protective layer 402 b acts as a durable,yet flexible, barrier when coated over silicone base layer 402 a orencapsulated about silicone core layer 404 a, significantly reducingundesired chemical reactions resulting in dissolution of the siliconeconstituent, which is commonly employed in the construction of a die-cutor molded gasket. Accordingly, composite seal 206, when formed, combinesthe benefits of both a, low-cost, low-durometer silicone with theimproved sealing and durability of a fluoroelastomer/fluoropolymer.

A method for forming composite seal 206 on bipolar plate 204 or MEA 202of a PEM fuel cell is described in conjunction with process flow 500 ofFIGS. 5A and 5B. Process flow 500 is initiated, at step 502, byreceiving one of the two aforementioned manufactured components (i.e., abipolar plate or an MEA) and loading, at step 504, said component into aholding fixture, a vacuum table, a magnetic chunk or any other suitablemechanism for stabilizing the manufactured fuel cell component. Forpurposes of brevity, the term “holding fixture” is used throughout torepresent any one of the aforementioned mechanisms. Informationpertaining to the manufactured fuel cell component and a correspondingapplication configuration parameter for depositing the constituents ofcomposite seal 206 may then be received, at step 506, by a chemicaldepositing system (not shown) for executing the process of depositingand treating the constituents of composite seal 206. A robotic gantrymay be used, for example, in depositing multilayer seal 206 along adesired periphery of manufactured fuel cell component, wherein therobotic gantry may be configured to accommodate a material deliverysystem for dispensing a liquid from of the required constituent.

Additionally, the depositing system may be configured to determine, atstep 508, whether application parameters received are in compliance witha manufacturer's sealing specifications. For example, predefinedmanufacturer's specifications pertaining to required sealing criteriaand the material composition of the manufactured fuel cell component maybe input into or made electronically accessible to the depositing systemfor determining whether the application parameters received by thesystem, at step 506, would render the manufactured fuel cell componentdeficient for its intended use. Additionally, if application parametersreceived by the depositing system are determined to be outside of themanufacturer specifications or, alternatively, manufacturerspecifications are not made available for the particular manufacturedfuel cell component loaded into the holding fixture, the system may befurther configured with a set of predefined checks to determine, atsteps 510 and 512, if received application parameters are acceptable. Ifit is determined that the application parameters received are notacceptable for the particular manufactured fuel cell component loadedinto the holding fixture, the depositing system may be configured toprompt for new application parameters, returning to step 506.

Upon receiving acceptable application parameters, the depositing systemis cued to deposit a constituent of composite seal 206. However, priorto depositing a constituent of composite seal 206, a determination mayfirst be made at step 514 as to whether an encapsulated ornon-encapsulated application of composite seal 206 is desired.

If, at step 514, it is determined that a non-encapsulated application isdesired, the manufactured fuel cell component loaded into the holdingfixture may receive, at step 516, a primer along the defined periphery,which is permitted to dwell. Thereafter, at step 518, an elastomercompliant layer (i.e., silicone base layer 402 a) is deposited along theprimed periphery of the manufactured fuel cell component. After theelastomer compliant layer is deposited, it may be cured and treated, atstep 520, using, for example, infra red radiation (IR), inductionheating, radiation ultra violet (UV) or any other suitable curingmethod. In a preferred embodiment, the elastomer compliant layer mayreceive any one of a plurality of surface treatments to prepare thesurface of the elastomer compliant layer prior to bonding of a thinprotective layer (i.e., fluoroelastomer protective layer 402 b), whichis to be coated thereon at step 522. The surface of silicone base layer402 a, for example, may be plasma treated to increase bond strength andsurface adhesion, wherein the foregoing is accomplished by convertingthe silicone surface to a carbonyl or carbonyl carboxyl crosslinkedsurface. In an alternative embodiment, the silicone surface may also beconverted to an amino-carboxyl or amino-carbonyl crosslinked surface.

Alternatively, at step 514, a determination may be made that anencapsulated application is desired. Similar to the non-encapsulatedapplication, the manufactured fuel cell component loaded into theholding fixture may first receive, at step 516′, a primer along thedefined periphery, which is permitted to dwell. Thereafter, at step518′, rather than receive an elastomer compliant base layer, a thinprotective base layer (i.e., fluoroelastomer protective layer 404 b) isapplied along the primed periphery of the manufactured fuel cellcomponent. The thin protective base layer is cured and treated, at step52W, before receiving, at step 522′, an elastomer compliant core layer(i.e., fluoroelastomer protective layer 404 a). The elastomer compliantcore layer may receive, at step 524′, any one of the previouslydescribed plurality of surface treatments to prepare the surface of theelastomer compliant layer prior to bonding of a thin top coat protectivelayer (i.e., fluoroelastomer protective layer 404 b′), which is to becoated thereon at step 526′.

Applications of the thin coat protective layer, whether in theencapsulated or non-encapsulated embodiment, are preferably achievedthrough dispensing a solvated solution of a fluoroelastomer orfluoropolymer constituent. Coating methods may include spraying or flowcoating of protective layer 402 b and 404 b/404 b′. After the solventhas evaporate, the thin fluoroelastomer or fluoropolymer protectivelayer is subject to a final dwelling and curing stage, at step 528, tocomplete construction of composite seal 206 on the select manufacturedfuel cell component.

The foregoing multilayer construction of composite seal 206 yieldshighly desirable attributes for PEM fuel cell applications and ensuresthe integrity of the seal over the entire periphery surface of primaryfuel cell components. Additionally, composite seal 206 directly disposedalong a particular periphery of bipolar plate 204 or MEA 202 allows fora thinner sealing construction to satisfy fuel cell stack tolerances,substantially increased resistivity to highly reactive chemical andthermal environments and a lower cost alternative to single compoundgaskets.

The foregoing description is provided for illustrating the principles ofthe present invention and it is foreseeable that various modificationscan be made by those skilled in the art without departing from thespirit and scope of the invention described herein. Therefore, oneskilled in the art will appreciate that the present invention can bepracticed by other than the described embodiments, which are presentedfor purposes of illustration and not by way of limitation, and thepresent invention is limited only by the claims that follow.

We claim:
 1. A composite seal, said composite seal comprising: a baselayer formed from an elastomer constituent; and a protective layerformed from a fluoroelastomer or fluoropolymer constituent, saidprotective layer applied over said base layer to coat said elastomerconstituent.
 2. The composite seal of claim 1, wherein said elastomerconstituent forming said base layer is substantially comprised of asilicone-based constituent.
 3. The composite seal of claim 1, whereinsaid fluoroelastomer or fluoropolymer constituent forming saidprotective layer is a solvated solution of a fluoroelastomer orfluoropolymer constituent, said solvated solution used to coat saidelastomer constituent forming said base layer.
 4. A composite seal, saidcomposite seal comprising: a base layer formed from a fluoroelastomer orfluoropolymer constituent; a core layer formed from an elastomerconstituent, said core layer deposited over said base layer; and aprotective layer formed from a fluoroelastomer or fluoropolymerconstituent, said protective layer applied over said core layer to coatsaid elastomer constituent.
 5. The composite seal of claim 4, whereinsaid elastomer constituent forming said core layer is substantiallycomprised of a silicone-based constituent.
 6. The composite seal ofclaim 4, wherein said fluoroelastomer or fluoropolymer constituentforming said base layer and said protective layer is a solvated solutionof a fluoroelastomer or fluoropolymer constituent, said solvatedsolution used to encapsulate said elastomer constituent forming saidcore layer.
 7. A method of constructing a composite seal on a component,said method comprising the steps of: loading said component into aholding fixture; applying a primer along a periphery of said component;dispensing an elastomer constituent directly onto said primed peripheryof said component, said elastomer constituent forming a base layer ofsaid composite seal; and applying a fluoroelastomer or fluoropolymerconstituent over said elastomer constituent, said fluoroelastomer orfluoropolymer constituent coating a surface of said elastomerconstituent to form a substantially thin protective layer over said baselayer.
 8. A method of constructing a composite seal on a component, saidmethod comprising the steps of: loading said component into a holdingfixture; applying a primer along a periphery of said component; applyinga first layer of a fluoroelastomer or fluoropolymer constituent directlyonto said primed periphery of said component; dispensing an elastomerconstituent directly over said first layer of said fluoroelastomer orfluoropolymer constituent, said elastomer constituent forming a corelayer of said composite seal; and applying a second layer of saidfluoroelastomer or fluoropolymer constituent over said elastomerconstituent, said second layer of said fluoroelastomer or fluoropolymerconstituent coating a surface of said elastomer constituent to form asubstantially thin protective layer over and encapsulate said corelayer.
 9. A method of sealing two component parts using a compositeseal, said method comprising the steps of: loading a first componentpart; applying a primer along a periphery of said first component part;dispensing an elastomer constituent directly onto said primed peripheryof said first component part, said elastomer constituent forming a baselayer of said composite seal; applying a fluoroelastomer orfluoropolymer constituent over said elastomer constituent, saidfluoroelastomer or fluoropolymer constituent coating a surface of saidelastomer constituent to form a substantially thin protective layer oversaid base layer; loading a second component part, wherein a periphery ofsaid second component part is aligned with said periphery of said firstcomponent part having said composite seal formed thereon; and joiningsaid second component part to said first component part along their saidperipheries, sealing said first component part and said second componentpart together.
 10. A method of sealing two component parts using acomposite seal, said method comprising the steps of: loading a firstcomponent part; applying a primer along a periphery of said firstcomponent part; applying a first layer of a fluoroelastomer orfluoropolymer constituent directly onto said primed periphery of saidfirst component part; dispensing an elastomer constituent directly oversaid first layer of said fluoroelastomer or fluoropolymer constituent,said elastomer constituent forming a core layer of said composite seal;applying a second layer of said fluoroelastomer or fluoropolymerconstituent over said elastomer constituent, said second layer of saidfluoroelastomer or fluoropolymer constituent coating a surface of saidelastomer constituent to form a substantially thin protective layer overand encapsulate said core layer; loading a second component part,wherein a periphery of said second component part is aligned with saidperiphery of said first component part having said composite seal formedthereon; and joining said second component part to said first componentpart along their said peripheries, sealing said first component part andsaid second component part together.